Abstract
The asymmetric unit of the title compound, bis-[4,4'-methyl-enebis(3,5-dimethyl-1H-pyrazol-2-ium)] β-octa-molybdate, (C11H18N4)2[Mo8O26] or (H4mbdpz)2[Mo8O26], is composed of an H4mbdpz(2+) cation and half of the β-octa-molybdate anion which is completed by inversion symmetry. The organic mol-ecular units are engaged in a series of N-H⋯O hydrogen bonds with neighbouring anions, with N⋯O distances and N-H⋯O angles in the ranges 2.730 (2)-2.941 (2) Å and 122-166°, respectively. These inter-actions lead to the formation of a supra-molecular two-dimensional network parallel to the (010) plane.